alpha channels support for 8-bit tiffs
added test for 4 channel tiff
* img_test is now tested for channel numbers instead of img
* fixed indentation to use spaces and trailing spaces
API of TiffDecoder back to what it was - normalizeChannelsNumber moved to protected
test code unified - channels number is tested for other formats as well
fixed tab indent
Merge pull request #462 from kobigurk:master